This invention relates to the laying of submarine pipelines. More particularly, the invention is directed to simultaneous trenching and pipe laying in an arctic environment.
Offshore oil production and storage facilities are typically linked to onshore facilities by at least one pipeline which has been laid upon the bed of a body of water. Because of the potential for vast offshore oil deposits in arctic regions many such pipelines will have to be constructed in bodies of water which are covered with a relatively thick ice mass for much of the year. Such pipe laying operations may take place during a winter season when the water is covered with a thick ice mass, or during a summer season when the water is open.
Arctic pipe laying operations which are restricted to the short open water season rarely provide sufficient time to lay a pipeline of appreciable length. Economic hardships are thus incurred as a result of delays in the flow of production revenues, and consequently, less opportunity for rapid installation cost reduction.
Alternatively, pipelaying operations conducted during an arctic winter season present the special problems associated with such a harsh environment. One noteworthy problem is that it is necessary to penetrate an ice mass of substantial thickness in order to gain access to the body of water in which the pipeline is to be laid. Moreover, it is often difficult to conveniently support the dredging and laying apparatus upon the ice mass or water.
There are several known techniques for arctic trenching and pipelaying. For example, U.S. Pat. Nos. 3,822,558, issued July 9, 1974, and 3,924,896, issued Dec. 9, 1975, each disclose an arctic-type pipelaying and burying arrangement. These patents disclose a buoyant platform, supported on a cushion of air, which is operable to form a slot in the ice through which ice laying and burying equipment extend. A trencher mechanism extends beneath the surface of the water from the bow end of the platform while a stinger for supporting the pipeline to be laid extends from the stern of the platform. Other arctic pipelaying arrangements are disclosed in U.S. Pat. Nos. 3,681,927, issued Aug. 8, 1972, 3,744,259, issued July 10, 1973, 3,844,129, issued Oct. 29, 1974, and 3,900,146, issued Aug. 19, 1975.
Conventional pipelaying and burying arrangements in which a pipeline or cable being laid passes through or across a trencher mechanism are disclosed in U.S. Pat. Nos. 734,615, issued July 28, 1903, 737,021, issued Aug. 25, 1903, 956,604, issued May 3, 1910, and 3,641,780, issued Feb. 15, 1972.
The methods and apparatus described in the prior art fail to provide convenient and reliable means for laying and burying pipe on the bed of a body of water covered with an ice mass. Moreover, the prior art fails to disclose a simultaneous method and apparatus for laying and burying a submarine pipeline in which the pipeline to be laid receives adequate support while submerged, but prior to being received in a trench
It is accordingly a primary object of this invention to provide a reliable method and apparatus for the simultaneous trenching and laying of a submarine pipeline. Another object of the invention is to provide a method and apparatus for trenching and laying a pipeline within a seabed during an arctic winter season in which the body of water is covered with an ice mass of substantial thickness. It is also an object of this invention to provide a novel apparatus for supporting simultaneous trenching and laying operation. A further object of this invention is to provide a submersible apparatus for conducting dredging operations while providing adequate lateral support for a submerged portion of the pipe. Other objects of this invention will be apparent to those skilled in the art upon reading this disclosure.